Error correction method for high density disc

ABSTRACT

An error correction method for optical discs, and more particularly, an error correction method appropriate to high density discs is provided. The error correction method adds inner parity and outer parity to an error correction block of size n byte x m x o. The method comprises the steps of obtaining a plurality of inner parity blocks (PI blocks) by segmenting the error correction block in the inner parity (PI) direction into x segments; generating e-byte PI for each of the plurality of PI blocks generated by segmenting, and adding e-bytes PIs to the PI blocks in the PI direction; and generating f-byte outer parity (PO) in the PO direction of the error correction block, and adding the POs to the PO direction. The error correction method enhances error correction capability while maintaining a redundancy of parity signal on a level similar to conventional DVDs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 09/612,971,filed Jul. 10, 2000 now pending. This application claims the benefit ofKorean Application No. 99-27453, filed Jul. 8, 1999, in the KoreanPatent Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an error correction method for opticaldiscs, and more particularly, to an error correction method appropriatefor high density discs.

2. Description of the Related Art

There are currently a variety of optical discs available, including acompact disc (CD), a digital versatile disc (DVD), and a high densityDVD (HD-DVD), which requires higher density recording and reproducingthan a DVD, and is currently under development. While a conventional DVDhas a storage capacity of 4.7 GB, the HD-DVD has a storage capacity of15 GB or more. The higher storage capacity of the HD-DVD is implementedby reducing the diameter of a beam spot for data recording/reproducingand increasing the line density.

The amount of data affected by a defect in an HD-DVD is far greater thanthe amount of data affected by the same length defect in a conventionalDVD. Therefore, an HD-DVD requires stronger error correction than aconventional DVD.

FIG. 1 shows the structure of an error correction code (ECC) block in aconventional DVD. The error correction code block shown in FIG. 1 has a10-byte parity for error correction of 172 bytes of data in the rowdirection, as an inner parity (PI), and a 16-byte parity for errorcorrection of 192 bytes of data in the column direction, as an outerparity (PO). Here, the capability of error correction by the PI is amaximum of 5 bytes, and that of the PO is a maximum of 16 bytes forerasure correction.

Assuming that an HD-DVD uses the same error correction method as aconventional DVD, the effect of a defect will now be explained indetail.

FIG. 2 illustrates the relationship of a beam spot and an object lens inan optical disc. Table 1 illustrates the relationships among t, thethickness of a disc, NA, the numerical aperture of an object lens, 2R,the diameter of a beam spot, and k, the length of a defect.

TABLE 1 k, length of t (mm) NA R (mm) 2R (mm) Remark defect 0.6 0.60.248 0.496 DVD k + 2R 0.65 0.273 0.546 0.3 0.65 0.136 0.272 0.85 0.1930.286 0.2 0.85 0.129 0.258 0.1 0.7 0.049 0.098 DVD/3.88 0.85 0.064 0.1281) The Effect of a Large Defect

Here, a large defect means a burst error which cannot be corrected by aPI, and is generated by a scratch, a finger print, a black dot, etc.

A defect which spans 5 bytes or more is a burst error which cannot becorrected by a PI. At this time, the length of a defect is k=5 bytes×16channel bits×0.133 Fm (the length of 1 channel bit)=10.64 Fm.

When a 20 GB HD-DVD is compared to a 4.7 GB DVD, the line densityincrease is (20/4.7)½. Accordingly, the same length defect damages 2.1times more data in an HD-DVD than in a DVD.

Though an HD-DVD seems to be more advantageous than a DVD due to theHD-DVD's smaller spot size, the stabilization time required forrestoring a reproduction signal (RF) in an HD-DVD is longer. Therefore,the effect of a spot size is thought to be similar in an HD-DVD and aDVD.

2) The Effect of a Small Defect

Here, a small defect means a burst error which can be corrected by a PI,and is generated by dust and the like. The length of the defect is equalto or less than 10.64 Fm.

According to table 1, when NA=0.85 and t=0.1 mm, the diameter of a beamspot incident upon the surface of an HD-DVD is 0.128 Fm, which is 1/3.88times that of a DVD with a diameter of the beam spot being 0.496 Fm.Therefore, the HD-DVD's probability of error occurrence by a smalldefect becomes 3.88 times greater than that of a DVD.

In addition, since the line density of an HD-DVD is 2.1 times greaterthan that of a conventional DVD, the probability of error in an HD-DVDis 8.148 times (3.88×2.1=8.148) greater than that of a DVD for the samesize defect. This means that when an HD-DVD uses the same modulationmethod as a DVD, error correction by a PI must be available for about40.74 bytes (5 bytes×8.148). Therefore, an HD-DVD requires a greatnumber of PIs.

In the previous DVD error correction method shown in FIG. 1, in order toraise the burst error correction capability, the number of data columnsmust be increased in the PI direction, while the number of data rowsmust be decreased in the PO direction.

However, when n, the number of data columns in the PI direction, exceeds256, a Galois Field operation GF(28) cannot be performed.

Thus, the previous error correction method in a DVD as shown in FIG. 1cannot be easily applied to HD-DVD.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide anerror correction method appropriate for an HD-DVD.

It is another object to provide a basic addressing structure appropriatefor the HD-DVD.

Additional objects and advantages of the invention will be set forth inpart in the description which follows, and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

To accomplish the above objects of the present invention, there isprovided an error correction method adding inner parity and outer parityto an error correction block having a size of n bytes x m x o, the errorcorrection method having the steps of obtaining a plurality of innerparity blocks (PI blocks) by segmenting the error correction block in aninner parity (PI) direction into x segments (here, x is an integer equalto or greater than 2); generating e-byte PI for each of the plurality ofPI blocks generated by segmenting, and adding the PIs in the PIdirection; and generating f-byte outer parity (PO) in the PO directionof the error correction block having PIs, and adding the POs in a POdirection.

It is preferable that the data frame, which forms an error correctionblock, is formed with two 2-KB user data blocks.

Also, it is preferable that the data frame has EDCs for correctingerrors in user data.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe preferred embodiments, taken in conjunction with the accompanyingdrawings of which:

FIG. 1 is the structure of an error correction code (ECC) block in aconventional digital versatile disc (DVD);

FIG. 2 illustrates the relationship between a beam spot and an objectlens in an optical disc;

FIG. 3 illustrates the relationships between an ECC block, an innerparity and an outer parity in the error correction method according toan embodiment of the present invention;

FIG. 4 illustrates the effect by an interleave between inner parity (PI)blocks in the same row;

FIG. 5 shows the process for performing an error correction methodaccording to the embodiment of the present invention;

FIG. 6 illustrates the structure of a data frame after it has beenscrambled in the error correction method of FIG. 5;

FIGS. 7A and 7B illustrate generation of inner parity and outer parityin an error correction block in the error correction method of FIG. 5;

FIGS. 8A and 8B illustrate the result of interleaving to the innerparity direction in the error correction method of FIG. 5;

FIG. 9 illustrates the result of interleaving the result shown in FIG. 8again in the inner parity direction; and

FIGS. 10A through 10D illustrate the result of interleaving in the outerparity direction in the error correction method in FIG. 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the present preferred embodimentof the present invention, examples of which are illustrated in theaccompanying drawings, wherein like reference numerals refer to likeelements throughout.

FIG. 3 illustrates the relationships between an error correction block,an inner parity (PI) and an outer parity (PO) in an error correctionmethod according to an embodiment of the present invention. As a methodfor improving a burst error correction capability in using the samenumber of parities, it is preferable that the number of data columns isincreased in the PI direction and the number of data rows is decreasedin the PO direction.

However, since a Galois Field operation cannot be performed when n, thenumber of data columns in the PI direction exceeds 256, the presentinvention uses a multi-way PI error correction method.

That is, n, the number of data columns in a row is divided into segmentswith an appropriate size (x), and then, an e-byte PI is added to eachsegmented PI block. Here, the size n/x is determined to be anappropriate size for adding a synchronous signal, and n, x, and e aredetermined so that n/x+e is less than or equal to 256.

If the number of data frames in the PO direction is 16, m (rows)×16+f(rows) is less than or equal to 256. Furthermore, x (the number of PIdirection segments), and f, (the number of PO direction parities), aredecided so that the result of multiplication of x with f is divided byo, the number of data frames, without a remainder. In this case, f canbe not equal to o, the number of data frames, unlike a conventional DVD,in which f is equal to o.

The error correction block shown in FIG. 3 causes a problem when theblock is recorded on a disc immediately after channel-modulation. Thatis, when a small defect occurs and e/2 bytes of data or more aredamaged, correction by a PI becomes impossible. Therefore, after addinga flag indicating that all data in the corresponding PI block is notcorrected, the data must be sent to an error correction process by a PO.When greater than or equal to f data is sent to a PO with a flagindicating that the data is not corrected by a PI, the PO cannot correctthe error either.

In order to effectively correct small defects and sporadically occurringerrors, interleaving is performed in the PI direction in x PI blocks.

FIG. 4 illustrates the effect of interleaving PI blocks in the same row.As shown in FIG. 4, even though a burst error occurs, the burst errorchanges into sporadic errors due to the interleaving between the PIblocks. Therefore, even when e/2 or more bytes of data are damaged, thenumber of errors are reduced to equal to or less than e/2 in a PI blockafter interleaving, and error correction becomes possible.

There is another method in which e-byte parity is added to each x-thdata in the same PI direction. In one method, interleaving is performedamong PI blocks in different rows in order to increase the interleavingeffect. In this method, however, there is greater delay between the timewhen error correction is completed and the time when data is output.Therefore, it is preferable that the scope of interleaving is determinedas a function of the delay and the size of burst defects to becorrected.

FIG. 5 shows the process for performing an error correction methodaccording to the embodiment of the present invention.

First, data for detection (IED) is added to address information (ID) 502to yield “ID+IED” 504.

Next, reserve space (RSV) for storing future scalability, userinformation, producer information, copyright protection, etc., and 4 KBuser data is added To “ID+IED” 504 to yield “(ID+IED) & RSV & 4 KB USERDATA” 506.

Next, 4 KB of user data is divided into 2 KB, considering compatibilityto an existing compact disc (CD) and a digital versatile disc (DVD), andthen, an error detection code (EDC) for detecting an error is added. Bydoing so, one data frame 508 is formed.

Next, in order to obtain data protection, channel modulation, and servocapacity, scrambling is performed on data frame 508. For example, inorder to properly perform scrambling of data on a 20 GB-level HD-DVDhaving 4 KB data frames and a 64 KB basic unit for error correction, thelength of the cycle of the random data generator in an HD-DVD having a64 KB basic unit for error correction and a 4 KB user data in one dataframe is designed to be 64 K, which is advantageous in suppressingdirect current (DC) component during servo operation and modulation.

FIG. 6 illustrates the structure of the data frame 510 after it has beenscrambled in the error correction method in FIG. 5. Referring to theexample in FIG. 6, data frame 510 is formed with a 4-byte ID, a 2-byteIED, an 18-byte RSV, two 2-KByte user data blocks, and two 4-byte EDCs.Here, one data frame 510 is 688 bytes in the PI direction (columndirection), and 6 rows in the PO direction (row direction).

Returning now to FIG. 5, one error correction block 512 is formed bygathering 16 data frames 510 shown, and a PI and a PO are added to theblock. This error correction block 512 then undergoes the steps of PI/POencoding and PI/PO interleaving to form recording block 514. Finally, asynchronous signal is added to recording block 514 yielding physicalblock 516, which is then recorded on a disc.

We now turn to FIGS. 7-10, which illustrate in detail the PI/PO encodingand interleaving of the present invention.

FIGS. 7A and 7B illustrate the generation of inner parity and outerparity in an error correction block shown as “4 way PI ENCODING\SINGLEPO ENCODING” in FIG. 5. Referring to FIGS. 7A and 7B, 16 data frames 510are lined up and then, four PIs, each of which have 8 bytes in the PIdirection, are added, and a PO, which has 12 byte to the PO direction,is added.

1) PO

PO is generated by using the Reed Solomon code RS(108, 96, 13).

That is, for data (B0,0˜Bi,j, i=0˜95, j=0˜687), B96,0˜Bi,j aregenerated.

2) PI

PI is generated by using RS(180, 172, 9).

That is, for data (Bi,0˜Bi,171, i=0˜107), Bi,688˜Bi,695 (i=0˜107) aregenerated; for data (Bi,172˜Bi,343, i=0˜107), Bi,696˜Bi,703 (i=0˜107)are generated; for data (Bi,344˜Bi,545, i=0˜107), Bi,704˜Bi,711(i=0˜107) are generated; and for data (Bi,546˜Bi,687, i=0˜107),Bi,712˜Bi,719 (i=0˜107) are generated.

Parties are generated in 4 ways in the PI direction so that no PIcorrection unit (including parity) exceeds 256, thus a GF (28) operationin a Galois Field can be performed. This also permits the addition ofcorrection incapability flags in four divided units for better erasecorrection in the PO correction process.

Furthermore, interleaving four PI blocks improves PI correctioncapability. In the present invention, such an error correction method isreferred to as Reed-Solomon multiple way PI or PO product code(RS-MWPC).

After PI/PO encoding, a burst error in the PI direction is changed intosporadic errors, and in order to protect PI and PO, interleaving isperformed in the PI direction. FIGS. 8A and 8B illustrate the result ofthis interleaving process, which is shown in FIG. 5 as “DATA INTERLEAVECOLUMN INTERLEAVE OF PI”. Referring to FIGS. 8A and 8B, data in four PIblocks is reallocated one by one in a predetermined turn in the datasection and the parity section.

FIG. 9 illustrates the result of interleaving the result shown in FIGS.8A and 8B again in the PI direction. PI divides each 8 bytes in the PIdirection and performs interleaving. This is to prevent occurrence ofburst errors in PIs.

When interleaving in PIs is completed, 12 rows including PO+PI paritiesfrom the 97th row to the 108th row are reorganized into 16 rows. Thereason why 12 rows including PO+PI parities can be reorganized into 16rows is that the result of multiplication of 4 (x), which is the numberof PI direction segments, by 12 (f), which is the number of PO+PI parityrows, is 16 (o), the number of data frames. To achieve this, 720 bytes(688+32) in the first PO+PI parity row is multiplied by ¾, and then, 540bytes become the first new PO+PI parity row, and the remaining720−540=180 bytes are passed to the second PO+PI parity row. The 180bytes are added to 720 bytes that are in the second PO+PI parity row,and then the first 540 bytes in the result of the addition are changedinto the second PO+PI parity row.

By doing so, the 12 rows are changed into a total of 16 rows of newPO+PI parity rows. By interleaving to the PO direction from the firstrow, all interleaving is finished and a total of 16 recording frames arereorganized as shown in FIGS. 10A and 10B. After inserting a synchronoussignal and performing channel modulation, this data is in a form thatcan be actually recorded on optical disc.

As described above, the error correction method according to the presentinvention enhances error correction capability in an HD-DVD whilemaintaining redundancy of parity code on a level similar to conventionalDVDs.

Although a few preferred embodiments of the present invention have beenshown and described, it would be appreciated by those skilled in the artthat changes may be made in these embodiments without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. A high density digital versatile disk (HD-DVD) for use in a recordingand/or reproducing apparatus, the disk including an error correctionblock structure to correct an error in the disk with the recordingand/or reproducing apparatus, the error correction block structurecomprising: a plurality of correction blocks, each correction blockbeing segmented into a plurality of data blocks of a predetermined sizeby the recording and/or reproducing apparatus; an outer parity matrixhaving a size of f data row provided at an end of a data block of theplurality of data blocks, in an outer parity (PO) direction by therecording and/or reproducing apparatus; and an inner parity matrixhaving a size of e data column provided at a side of the data block, inan inner parity (PI) direction by the recording and/or reproducingapparatus, wherein the data block having the outer parity matrix and theinner parity matrix is recognized by the recording and/or reproducingapparatus so as to correct the error, wherein when x is a number of thesegmented data blocks, o is a number of data frames in the PI directionin the corresponding segmented data block, and f is a number of datarows in the outer parity matrix, a result of multiplication of x with fis divided by o without a remainder.
 2. The optical disk of claim 1,wherein the high density digital versatile disk has a storage capacityof at least 15 GB.
 3. A high density digital versatile disk (HD-DVD) foruse in a recording and/or reproducing apparatus, the disk including anerror correction block structure to correct an error in the disk withthe recording and/or reproducing apparatus, the error correction blockstructure comprising: a plurality of correction blocks, each correctionblock being segmented into a predetermined size by the recording and/orreproducing apparatus forming a plurality of data blocks; a plurality ofinner party blocks, each inner parity block being added to acorresponding data block of the plurality of data blocks by therecording and/or reproducing apparatus, in inner parity direction; and aplurality of outer parity blocks, each outer parity block being added tothe corresponding data block of the plurality of data blocks in a columndirection by the recording and/or reproducing apparatus, wherein eachdata block comprising the corresponding inner parity block and outerparity block are recognized by the recording and/or reproducingapparatus so as to correct the error, wherein when x is a number of thesegmented data blocks, o is a number of data frames in a PI direction inthe corresponding segmented data block, and f is a number of data rowsin the outer parity block, a result of multiplication of x with f isdivided by o without a remainder.
 4. A method of obtaining an errorcorrection block for an information storage medium, the methodcomprising: segmenting a correction matrix into a plurality of segmenteddata matrices in the inner parity direction; generating inner paritymatrices having a first size and outer parity matrices having a secondsize; and adding an inner parity matrix and an outer parity matrix to acorresponding segmented data matrix of the plurality of segmented datamatrices in the inner parity direction and the outer parity direction,respectively, wherein when x is a number of the segmented data matrices,o is a number of data frames in the PI direction in the correspondingsegmented data matrix, and f is a number of data rows in the outerparity matrix, a result of multiplication of x with f is divided by owithout a remainder.
 5. The method of claim 4, wherein when x is anumber of PI direction data columns in the corresponding data matrix,and y is a number of PI direction data columns in the inner paritymatrix, a condition x+y≦256 is satisfied.
 6. The method of claim 4,wherein when p is a number of PO direction data rows in thecorresponding data matrix, q is a number of PO direction data rows inthe outer parity matrix, a condition p+q≦256 is satisfied.
 7. The methodof claim 4, further comprising interleaving the plurality of datamatrices having added both the inner parity matrices and the outerparity matrices in a PI direction.
 8. The method of claim 4, wherein anumber of PI direction data columns of the error correction block isequal to or greater than 256.